An Aplysia preparation has been developed in this laboratory in which the neurophysiology of behavior can be analyzed. We have identified neurons which control the parameters characterizing habituation, i.e., response decrement, spontaneous recovery, and dishabituation. Both the peripheral and central nervous systems regulate the parameters of habituation, and the regulation each exerts can be differentiated. Habituation, which may be an archetype of learning, involves comparatively simple neural networks, and is amenable to physiological and behavioral analysis. The objectives are: 1) To show the physiological properties and behavior which are distinctively attributable to the central nervous system and those which are attributable to the peripheral nervous system. 2) To determine the neural network necessary for controlling habituation and its associated parameters; a model of the network resulting from previous studies will guide this effort. The network may be a basic component of those involved in more complex behaviors. 3) To investigate changes in synaptic efficacy during habituation and to evaluate specific mechanisms, such as inhibition. Inhibition appears to be involved in central and peripheral control of habituation. 4) To correlate neural coding with the parameters characterizing habituation. The analysis should indicate those electrophysiological properties essential for response decrement, dishabituation, and spontaneous recovery. 5) To examine the neural events which underlie retention of habituation. It is felt that retention is a form of memory, and the physiological events could be common to both.